I'm working with a Nissan Z24i I4 gas engined 4x4 that I hope to coax 25 mpg mixed from.
Baseline is around 20 mpg mixed. Have it up to almost 22 mpg mixed.
All I've done so far is to change out the gear oil in everything and add a moly additive. Moly in new engine oil and new plugs/cap/rotor. Fixed a sloppy timing chain. Upped the tire pressures.
For your diesel might try:
* Condensator or PCV jar
* acetone or Diesel Kleen with Cetane Boost
* moly additives in gear oil and engine
* spiral muffler
http://www.spiralturbobaffles.com/semiinfo.html
* fuel heater and 195F thermostat
* airtabs
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Leading the perpetually ignorant and uninformed into the light of scientific knowledge. Did I really say that?
a new policy....I intend to ignore the nescient...a waste of time and energy.